A single light-emitting diode chip generally has a forward voltage of 1V˜4V, and the packaged light-emitting chip has a forward voltage of 2V˜5V. To be adapted to the 100V or 220V power line, the “step down converter” or the “series light-emitting diode” means is usually introduced to the light-emitting diode.
The step down converter is an external down-converting component which can be coupled to the light-emitting diode in order to adjust the voltage drop across the light-emitting diode to comply with its work voltage.
The series light-emitting diode is the light-emitting diodes that are serially-connected with each other. The voltage drop across each light-emitting diode can be controlled by adjusting the number of the light-emitting diodes. Generally, if 110V main power and 3.5V voltage drop per light-emitting diode are used, a total of 30 light-emitting diodes in series are needed in order to keep the working voltage across each light-emitting diode around 3.5 V.
Nevertheless, the down converter imposes an extra burden on user. In addition, with the improvement of the luminous efficiency of the light-emitting diode chip, less series light-emitting diodes are needed to reach the luminance required in lighting. As shown in the table in below, according to the forecast of Optoelectronics Industry Development Association (OIDA), LED's luminous efficiency can reach 150 μm/W by 2012. If the forecast is correct, with the increase of the luminous efficiency, the use of much less light-emitting diodes can reach the luminance as the fluorescent lamp does. For example, to generate light of 3400 μm, 17 light-emitting diodes are used in 2007, while only 2.3 light-emitting diodes are used in 2020. In other words, in the infrastructure of the present power line system (100V˜220V), a great voltage mismatch exists between the high efficiency light-emitting diode and the power line.
SSL-LED SSL-LED SSL-LED Technology200720122020FluorescentLuminous efficacy 7515020085(lm/W)Flux (lm/lamp)200100015003400Input power (W/lamp)2.76.77.540Equivalent Quantity 173.42.31(LED)